In the manufacture of conventional silver halide photographic materials, photographically useful reagents which are substantially water-insoluble {for example, oil-soluble couplers, antioxidants to be used for prevention of color-fading, color-fogging or color-mixing (such as alkylhydroquinones, alkylphenols, chromans, coumarones), hardening agents, oil-soluble filter dyes, oil-soluble ultraviolet absorbents, oil-soluble brightening agents, DIR compounds (such as DIR hydroquinones, colorless DIR couplers), developing agents, color developing agents, DDR redox compounds, DDR couplers} are incorporated into the hydrophilic organic colloid layers (for example, light-sensitive emulsion layer, filter layer, backing layer, antihalation layer, interlayer, protective layer), whereupon the reagent is first dissolved in an appropriate oil-forming agent or a high boiling point solvent and the resulting solution is dispersed in a hydrophilic organic colloid, especially a gelatin solution, in the presence of a surfactant. As the high boiling point solvent, phthalic acid ester compounds and phosphoric acid ester compounds are advantageously used.
Phthalic acid ester compounds and phosphoric acid ester compounds have been the most widely used for this purpose, because they have excellent dispersant properties with respect to couplers, a high affinity for colloid layers such as gelatin, a favorable influence on the stability of the color images formed, the influence on the hue of the color images formed and the chemical stability in photographic materials, and additionally are easily and inexpensively available.
However, these known high boiling point organic solvents (for example, phthalic acid ester compounds and phosphoric acid ester compounds) have been found insufficient in terms of their capacity to prevent the color images from being faded or stained due to the effects of light, heat or humidity.
The high boiling point organic solvents used in photographic materials are required to have many requirements. For instance, they must be prepared easily and inexpensively, have excellent solubility and dispersion stability properties with respect to photographic reagents, have no adverse influence on the ease of development and photographic properties, have excellent stability and have no adverse effect on the environment, they must have excellent ability in preventing the color images formed from being faded and have excellent chemical stability.
At the current time, processing for development of photographic materials is being directed to rapid processing, simple processing, processing with small replenishment (including the amount of rinsing water) and dispersed processing, rather than central processing. Accordingly, the problem of reduction fading during bleaching or bleach-fixation of cyan dyes is being focused on. It is believed that the reduction fading is caused by reduction of the iron(III) ion complex into an iron(II) ion complex in the bleaching or bleach-fixation bath because of the developing agent as brought into the bath together with the photographic material being processed or by reduction of the cyan dye into a colorless leuco dye because of the iron(II) ion complex as increased by fatigue of the bleaching or bleach-fixing bath. Accordingly, the high boiling point organic solvents used in photographic materials have been further required to have an activity of inhibiting the reduction fading of cyan dyes.
JP-A-62-134642 (the term "JP-A" as used herein refers to a "published unexamined Japanese patent application") mentions phthalic acid esters having a bulky substituent in the ortho-position, and European Patent (EP) 228,064 A2 mentions phthalic acid esters of tertiary alcohols. Both references disclose that the respective solvents have an activity of inhibiting reduction fading of cyan dyes caused by iron(II) ion. The former is different from the present invention in that this does not use any benzoic acid esters but uses phenol esters and the latter is different from the present invention in that this uses esters of monohydric alcohols.
The compounds mentioned in the aforesaid two patent publications have an activity of inhibiting reduction fading of cyan dyes caused by iron(II) ion, but the activity has been found to be small and insufficient for photographic purpose. Accordingly, an extremely large amount of the compounds would have to be added in order to attain the desired effect and thus are not always commercially practical.